Austria didn’t intervene, either. Nor did Prussia. Also the Papal States chose to stay out of it. Savoy was right out. Bavaria took a pass, as did Saxony. The Dutch? No deal. Likewise, Sweden supplied no mercenary troops to Great Britain.
I could go on.
I get that the subject of Russian interference in American politics is of interest right now. This writer is really, really reaching. This was never a real possibility. Catherine disliked George and often treated British diplomats poorly. She and her government felt that George had wronged the Americans and he was getting his just deserts. She also felt that the Americans winning might be to Russia’s advantage.
Beyond that, Russia had no tradition of hiring out its troops as auxiliaries. The German princes did. They’d done it extensively for the British throughout the 18th century. This was a Hail Mary on the part of the British that they didn’t really expect to succeed. The reporter is vastly overstating the significance.